The invention relates to a brush, in particular a brush for applying a cosmetic product to keratinous fibers, especially for applying a mascara to the eyelashes or a dye to the hair, and to a make-up device which comprises this brush and has a substantially plano-convex profile.
Conventionally, a brush for applying a cosmetic product comprises an elongate core formed by helically winding two branches of a metal wire and bristles implanted radially in this core and gripped between these wound branches. Such brushes may be of various shapes and may have cutouts. If these brushes are used for applying mascara to the eyelashes, such shapes and such cutouts are provided in order to make it possible to obtain more or less heavy make-up or a greater or lesser elongation and curving of the eyelashes.
The prior art, for example FR-A-2715038, discloses mascara brushes having a substantially convex shape, such as for example the shape of a rugby ball, a flat notch having been cut out in the brushes over their entire length. Since the bristles of the flat notch are short, they are wiped off only slightly on exit from the reservoir containing the mascara; such brushes provide very heavy make-up.
Brushes are also known having the shape of a portion of a torus, these brushes being obtained by twisting the core of a cylindrical brush in an arc of a circle. Such brushes have a convex face, a concave face and two substantially plane faces. Such brushes are not very easy to handle; in fact if the user rotates the stem of such a brush about its axis between her fingers, for example in order to apply a product to the eyelashes, she must continually correct the distance between the brush and the eyelashes. Moreover, it was found that such a brush loaded the eyelashes, but without smoothing them sufficiently. Brushes obtained by twisting the core of a cylindroconical brush in an arc of a circle have the same disadvantages.
Although these conventional brushes give substantially satisfactory results, it is desirable to have brushes which take good hold of the eyelashes in order to ensure effective smoothing of the product, good separation of the eyelashes, and a relatively light make-up. It is therefore an object of the invention to provide a brush useful for the simple, economical and practical application of makeup.
To this end, the invention provides a brush for applying a cosmetic product which, when used to apply mascara to the eyelashes, make it possible to obtain make-up which is natural, that is to say relatively light, but with the lashes appreciably lengthened, these brushes, moreover, being very easy to handle.
According to a first aspect of the invention, the brush comprises a straight stem defining a main axis; a flexible core comprising a first and a second end, the first end being integral with this stem; and bristles implanted radially in this core, the ends of the bristles defining the surface of the brush, this surface comprising a first face. The intersection of any plane which passes through the main axis, herein called the meridian plane, with the surface of the brush defines two convex curves (i.e., their concavity faces the inside of the brush) called peak lines, having a specific curvature. The first face is substantially straight and parallel to the main axis.
The curvature of each peak line is the reciprocal: l/r of its radius of curvature r. At each point of the core, the intersection of the surface of the brush with any plane perpendicular to the core defines a cross-section of the brush. Preferably, the core is centrally positioned in each cross-section of the brush. The faces are longitudinal portions of the surface of the brush.
Preferably, the surface of the brush comprises at least one second face, called a face of maximum curvature, at which the curvature of the peak lines passes through a maximum in the region of this second face.
Advantageously, the curvature of the peak lines has a single maximum. Preferably, the surface of the brush comprises a single straight face. More preferably, the curvature of the peak lines increases continuously from the straight face to the peak line of maximum curvature. Preferably, the face of maximum curvature and the straight face are diametrically opposite one another with respect to the core. Advantageously, the bristles of the same cross-section are all of the same length.
According to a second aspect of the invention, the brush is manufactured by the steps of forming a starting brush having a straight stem, and imparting a curve to the core in said meridian plane, said curve having a curvature substantially equal to the curvature of one of the two meridian lines of said meridian plane and being in an opposite direction to the curvature of one meridian line.
At each point of the core, the intersection of the surface of the starting brush with any plane perpendicular to the core defines a cross-section of the starting brush. Preferably, the starting brush is selected in such a way that the core is central in each cross-section of the starting brush.
The surface of the starting brush is thus modified in that one meridian line is converted into a substantially straight peak line, and the curvature of the second meridian line belonging to the same meridian plane is increased substantially. The core remains central in each cross-section of the brush, but these cross-sections are no longer parallel.
Desirably, a twist is imparted to said first end of the core in order to align the second end of the core with the main axis. The brush may thus be used with a mascara reservoir equipped with a wiper of conventional design.
Preferably, one of the meridian planes of the surface of the starting brush is a plane of symmetry of the starting brush. If appropriate, the starting brush comprises a plane of symmetry perpendicular to the axis of the core.
Preferably, the surface of this starting brush is a surface of revolution. Advantageously, each cross-section of the starting brush is convex.
This brush is perfectly suitable for making up eyelashes, and therefore a third aspect of the invention provides a make-up device comprising a mascara reservoir and a brush according to the invention for the application of mascara.
The brush according to the invention has a continuous evolute profile which is plano-convex in relation to its main axis, i.e., when the brush executes a revolution about its main axis, for example when the user rotates the stem of the brush between her fingers, it evolves from a substantially plane face, which surrounds the straight peak line parallel to the main axis, towards a convex face of increasing radius of curvature, to reach maximum curvature, then decrease and return to a plane face.
The substantially plane profile is located in the concavity of the brush. Since each cross-section is perpendicular to the core at any point of the latter, the bristles of the brush have a density higher than the rest of the brush along this plane profile. Moreover, these bristles converge. The density of the bristles decreases progressively from the plane face to the face of maximum curvature. Preferably, the face diametrically opposite the straight face with respect to the core is that having the greatest curvature. This face thus has a much lower bristle density, and these bristles diverge.
When the user uses this brush in order to apply a make-up product to the eyelashes, she extracts the brush from the product reservoir, the brush passing through a wiper. If the bristles in the same cross-section are all of the same length, they are all wiped. However, the face comprising a substantially plane profile is wiped to a lesser extent because the bristles converge and are very dense. By contract, the face having the greatest curvature is wiped to a greater extent, since the distribution of the bristles is highly spaced out. The user places the brush against the eyelashes and rotates it between her fingers: the brush loads each eyelash with product by means of its plane profile, then it combs the eyelash, lengthens it and curves it by means of the rest of its surface. The make-up thus obtained is relatively light, and the lash appreciably lengthened and highly curved.
Furthermore, the bristles of a brush according to the invention may be of any type: they may be bristles of different lengths, of different diameters or different cross-sections and of different materials, bristles with tapered ends, fork-shaped ends or ends in the form of a pinhead, or bristles which have undergone any kind of treatment known in the art.
There may also be provision for the brush according to the invention to comprise alternate rows of short bristles and long bristles, the long bristles alone defining the surface of the brush. Such a version of the invention makes it possible to increase the loading of the eyelid with product.
The helical winding of the two branches of the metal wire forming the core may be provided so as to have a right-hand pitch, as is conventional in the manufacture of make-up brushes, or a left-hand pitch, as taught by FR-A-27011098. To manufacture a brush with a left-hand pitch, the branches of the core are twisted by rotating them to the left in order to form turns which rotate clockwise around the core, starting from the stem and advancing towards the end of the brush.
The brush with a left-hand pitch is preferred for the production of brushes according to the invention: this gives the bristle turns an orientation which makes it possible to separate the eyelashes more effectively during make-up.